Study of the biomechanics of the bone structure of feet has revealed that, while everyone has a so-called "neutral position" of the rearfoot complex of the bones in their feet, this neutral position will vary from person to person. The neutral position of the rearfoot complex long has been known to be the position at which the foot is neither pronated nor supinated. When the foot is in the neutral position, it is oriented in the most efficient position to accommodate the full range of foot rotation during locomotion (walking, running, skiing, etc.). The weight of the individiaul is supported by the bone structure of the foot most effectively and with the least stress on muscles in the foot and leg when the foot is in the neutral position. The neutral position does not necessarily occur when the calcaneous bone (heel bone) is vertically aligned with the tibia and fibula (leg bones).
Understandably, but unfortunately, the manufacture of ready-to-wear shoes and ski boots, and even customized shoes and boots, largely has disregarded the variation from individual to individual of the neutral position. Thus, everyone is assumed to have the same general neutral position, usually when the plantar surface is horizontal and the calcaneous bone is vertically aligned with the tibia and fibula. This simplistic approach is adequate for most of the population under most conditions, but there are a growing number of situations in which this approach causes or exacerbates problems.
First, those individuals who have neutral positions which deviate substantially from the assumed "normal" neutral position can experience considerable discomfort during standing, walking, running or skiiing when wearing ready-to-wear shoes or ski boots. The construction of these shoes or boots will displace the rearfoot complex of the foot from the neutral position for that individual and place extra stress on the foot muscles.
A second area that has gained significance is in connection with athletics. Small deviations from the assumed "normal" neutral position occur in almost everyone, and these deviations can become significant and cause substantial discomfort if the foot is subjected to high stress, for example, as a result of jogging, running or skiing.
There are at least ten million people in the United States who are involved to some degree in running, jogging, or skiiing, and the number is constantly growing. While a significant number of these people participate in competitive athletics, the vast majority participate for their own satisfaction and/or heath. Even the non-competitive athlete, however, will engage in many repetitions of his sport during the course of a year. Unfortunately, the equipment, and particularly ready-to-wear shoes and boots, can combine with an athlete's enthusiasm for his sport to produce a wide range of injuries or maladies. Thus, arch strain, heel spur syndrome, runner's knee, shin splints, tendonitis, upper leg and hip strain and even lower back problems can be, and often are, detrimental "side effects" of highly bereficial cardio-pulmonary exercises of jogging, running and skiiing.
There are currently a myriad of different ready-to-wear shoes and ski boots which are recommended and extensively advertised as being designed specifically for running or skiing and the problems associated therewith. Each year, e.g., RUNNERS' WORLD publishes an issue of their magazine devoted exclusively to the evaluation of various brands of running shoes. While the evaluation is interesting, it involves a high degree of subjectivity. Commerically available running shoes generally follow relatively conventional formulae in their construction, with cosmetics being as important as almost any other factor in inter-brand competition.
The biomechanical aspects of running and other footbased athletic endeavors have been studied in some detail. In the January, 1974 issue of the journal of the American Podiatry Association the biomechanical basis of skiing and the affect of deformities or irregularities in the bone structure of the foot were studied, particularly in connection with the desirability of canting the ski boot and using in-boot orthotic devices. The book entitled THE FOOT BOOK, ADVICE TO RUNNERS examines the biomechanics of walking, jogging, running and sprinting, together with the effect of abnormalities of the neutral position of the rearfoot complex of the bone structure on these biomechanical functions.
These articles conclude that orthotic devices, positioned in the shoe of the runner by a podiatrist, can be of significant assistance in overcoming and eliminating chronic runner's foot, knee and leg problems. Such orthotic devices may include rearfoot posts, arch supports and forefoot canting devices, to name a few. Similarly, podiatrists have used in-shoe orthotic devices to enable non-athletes with severe variation from the normal neutral position to stand and walk comfortably. The effort in connection with orthotic devices is to attempt to position the foot in so-called "neutral" position. Thus, orthotic devices seek to bring or build the inner sole of the shoe up to the foot, when it is in the neutral position, and to have the foot function around this neutral position.
When this alignment or support of the foot is accomplished by an orthotic device mounted inside the shoe, care has to be taken that the combination of the orthotic devices and the shoe or produces the desired result. Many running shoes, e.g., do not come in variable widths and will not have sufficient room to accommodate an orthotic device. Sometimes the flexibility of the orthotic device must be varied so that the combined flexibility of the orthotic device and the shoe is optimal. These problems usually eventually can be overcome to a major degree by a podiatrist through variation of the orthotic appliances and the running shoes employed by the runner, but the care and assistance of a trained professional usually is required. Most runners, however, do not go to the podiatrist until the maladies are severe, and all would prefer to avoid a post-injury experimentation experience.
Another approach to the problem of providing a better shoe or boot for ordinary or athletic use has been to custom mold the shoe, boot or inner boot bladder around the foot of the wearer. It has been believed to be particularly useful to be able to support the entire bottom or plantar surface of the individual's foot by custom molding an insole to that surface. The shoe, boot or bladder upper can be molded or otherwise formed to conform to the specific configuration of the upper part of the foot of the user. The patent literature is replete with molding processes for the formation of shoes that are customized to an individual's foot, and the following United States patents are typical of such prior art processes: U.S. Pat. Nos. 2,961,714, 2,955,326, 2,961,714, 2,955,326, 2,907,067, 2,877,502, 2,856,633, 2,572,680, 2,568,292, 2,547,419, 2,332,000, 2,177,304, 2,120,987, 1,646,194.
While these prior art processes describe various methods and techniques for obtaining an impression of the human foot and forming a shoe based upon such an impression, the thrust of these processes is to obtain better foot support which mates with the bottom surface of the foot, and little or no consideration is given to the relative movement of the sketetal structures of the rear foot.